1. Field of the Invention
The present invention relates to a relay communication system for realizing a multiple address communication by repeating a point to point data transfer a plurality of times.
2. Description of Related Art
As a communication system for performing a multiple address communication, a relay communication is known, in which a multiple address communication is realized by performing a data transmission between a communication terminal and another communication terminal and repeating this between a plurality of communication terminals sequentially to relay a data (inter-point asynchronous communication). In such relay communication system, an originating communication terminal confirms whether or not the data is received by all of other communication terminals in the same link, by response from the last communication terminal of the link.
In general, in a case where a communication is performed by utilizing circuits having different data transmission rates, maximum transfer unit (MTU) may be different every circuit. In the usual communication control system, when the MTU is different on a communication path, data may be divided or combined by performing a fragmentation, etc. In the usual circuit, however, it is necessary to wait for a response of data reception in order to confirm whether or not data can be received. Such waiting for the reception response may cause the communication efficiency to be very low when looked from the originating communication terminal. In a circuit in which a delay time is increased due to fragmentation, etc., even when a fixed level, preceding control is used, the circuit can not be used efficiently since a next transmission must be suspended until a response of data reception is received, even when data is normally being transmitted.
On the contrary, in the relay communication system, a repeating communication terminal transmits a data reception response to a transmitting terminal immediately after the repeating terminal confirms a reception of data. Since, in this system, the transmitting terminal always transmits data to a next communication terminal, the communication circuit can be used efficiently. In this case, however, it is impossible due to delay caused by the inter-circuit relay to confirm whether or not the transmitting terminal a normally transmit data to the receiving terminal. Therefore, each communication terminal confirms whether or not the relay communication between it and a next communication terminal is normally, completed by monitoring the next communication terminal next even after the communication to the next communication terminal is ended.
In such conventional relay communication system, in order to confirm whether the relay communication is normally completed on the side of the transmitting terminal, the first, transmitting terminal must wait for the response from the last communication terminal and, therefore, the status of the link must be monitored during the relay communication is being performed, by securing the link. However, when a data transmission is performed through circuits having different transmission rates (for example, a transmission rate inside a protocol transformation device such as a gateway is different from that outside the gateway in a network connected through the protocol transformation device) and a large delay occurs due to data error, etc., a transmitting communication terminal can not get hold of the delay time caused by a multiple address communication. Therefore, it is necessary to continuously transmit data for checking the status of the link (for checking an operation of the other side terminal caused by a frame transfer) for a time period necessary to get hold of the delay time and, thus, the coefficient of utilization of the circuit is lowered.
An object of the present invention is to provide a relay communication system capable of optimally controlling the usage of circuit during a delay time which occurs when a relay communication (receiving control and transmission control) is performed asynchronously between communication terminals and capable of tightening a management of the status of communication. Another object of the present invention is to provide a guaranty and monitor method for data transfer and a communication terminal using the same method.
In a first aspect of the present invention, a relay communication system in which a multiple address communication is realized by repeating a point to point communication a plurality of times, comprises means for uniquely identifying a transmitting data on a network on the basis of an identifier of a communication terminal of a transmitting station and an identifier of the data, means for recognizing the progression of relay communication from the transmitting station when a receiving station is performing a relay transmission, means for obtaining a delay time until a receiving terminal giving the latest response by measuring response times from the communication terminal of the transmitting station and means for determining a transmission timing of data for checking an end of the relay communication, according to the delay time.
According to a second aspect of the present invention, the communication terminal used in the above mentioned relay communication system comprises a receiving control portion for receiving data in frame unit from a receiving communication circuit, a transmission control portion for transmitting data in frame unit from a transmitting communication circuit, a memory portion for temporarily storing the receiving data, a time management portion for managing an internal time and burying time stamps in the receiving frame and the transmitting frame, a destination management portion for managing destinations, a data identification portion for uniquely identifying a communication to which the frames belong, on the basis of the communication identifier and the transmitter identifier in the frame, to obtain the address from the destination management portion and storing the address in the memory portion, a delay management portion for measuring a delay time due to a relay communication by transmitting a monitor frame and receiving a response frame at a constant interval through the transmitting control portion and the receiving control portion and a main control portion for controlling the whole communication terminal.
The destination management portion may include a destination management information table for registering a transmitter identifier information indicative of an identifier number of the transmitting communication terminal, which is uniquely determined in the network, a communication identifier information indicative of an identifier number of a communication managed in transmitter unit, a phase number information which is a value indicative of the progression of the communication, a destination information indicative of addresses of communication terminals of the respective destinations, a delay information obtained by a difference between a transmitting time instance and a response time instance indicated in the response frame and a phase number information.
In a case where this communication terminal is used as the transmitting station, the relay communication system may be constructed in such a way as described below. When data is inputted to the memory portion, the transmission control portion starts a data transmission under control of the main control portion. The transmitting station transmits a link connection frame to a first receiving station of addressed receiving stations and, when the transmitting station receives an acknowledge response from the receiving station, it is confirmed that the connection to the receiving station is established. Upon the established connection to the receiving station, the transmitting station starts to transfer data to the receiving station by burying an address in an address assignment frame. When the transmitting station receives an acknowledge frame from the receiving station, it is confirmed that a notice of address is completed. The delay management portion obtains a delay time from a difference between a transmission time and a response time contained in the response frame with respect to the acknowledge response from the receiving station and start a timer corresponding to the delay time. When the timer times up, the transmitting station transmits a delay inquiry response frame, it transmits a delay inquiry response frame. In a case where the delay inquiry frame is not transmitted, it transmits a data frame. When the transmitting station receives a delay response frame from the receiving station in response to the delay inquiry frame, it registers the delay time in the delay response frame in the delay management portion. Thereafter, the transmitting station transmits the delay inquiry frame every delay time. After the transmission of all data frames is completed, the timer corresponding to the delay time is started. When this timer times up, the transmitting station transmits a delay inquiry frame and waits for a delay inquiry response frame. When the progression of relay communication notified by the delay inquiry frame indicates an end of communication, the communication is deemed as being normally ended and the transmitting station transmits a link cut frame. When the transmitting station receives an acknowledge response frame thereto, the communication is ended.
In a case where the communication terminal is used as a receiving station, the communication system may be constructed in such a way as described below. When receiving control portion receives a link connection frame, the receiving station starts a receiving operation by transmitting an acknowledge response frame in response to the link connection frame. When the receiving station receives a destination assignment frame, it notifies the destination management portion of the destination assignment frame, extracts a real data from the data frame received by the receiving control portion and writes it in the memory portion. When the data frame is received, a response time is set in the acknowledge frame and the latter is transmitted. When the link cut frame is received, a completion of communication is noticed to the main control portion and an acknowledge response frame is transmitted to end the communication. When the communication terminal is used as a relay station, it operates as the receiving station with respect to the transmitting station and as the transmitting station with respect to the destination station.
According to a third aspect of the present invention, a data transfer guaranty monitor method in a relay communication system in which a multiple address communication is realized by repeating a point to point communication a plurality of times comprises the steps of uniquely identifying a transmitting data on a network on the basis of an identifier of a communication terminal of a transmitting station and an identifier of data, recognizing in real time a relay transmission by recognizing the progression of the relay communication from the transmitting station when a receiving station performs the relay transmission, measuring a response time of the other side of the communication by the communication terminal of the transmitting station to obtain a delay time of a receiving station whose response is the latest to thereby measure a delay time caused by the relay communication and determining a data transmission timing for checking an end of the relay communication according to the delay time.
In this method, the delay time with respect to the receiving station can be calculated by setting a transmission time information indicative of a transmission time of an information frame, setting the transmission time information in the information frame and a response time information indicative of a transmission time of a response frame corresponding to the information frame sent from the receiving station to the transmitting station in the response frame and obtaining in the transmitting station a difference between the transmission time and the response time information set in the response frame.